Generic hydraulic dampers serve to dampen impacting forces such as impacts on structural elements. Generic hydraulic dampers are, for instance, used to dampen vibrations in structures such as bridges or high rise buildings that may occur during earthquakes. Hydraulic dampers are, for instance, used for this purpose in cable dampers. Generic hydraulic dampers are designed to mitigate the danger that sudden impact may separate supporting structural elements. Generic hydraulic dampers are correspondingly designed to dampen such impacts. Due to the considerable forces occurring in the area of application of such hydraulic dampers, these dampers must be constructed particularly robust to be able to dampen extremely high forces. Over and above this, such hydraulic dampers are also required to be particularly robust and reliable and this must be taken into consideration in the design of such hydraulic dampers.
Generic hydraulic dampers generally have a working chamber with a sliding piston dividing the working chamber into two sub-chambers, viz. a first and a second sub-chamber. The piston will have a fluid line with a small cross-section connecting the two sub-chambers to allow the flow of fluid between said sub-chambers. The hydraulic damper is to be fitted between the elements of two structures to be dampened against each other with the piston fastened to the first structural element and the enclosure with the working chamber fastened to the second structural element. The working chamber is filled with a hydraulic fluid. A force acting to cause relative movement between the two structural elements will slide the piston in the working chamber to thereby change the ratio of fluid volumes in the two sub-chambers. The small cross-section of the fluid line in the piston ensures dampening of the relative movement of the structural elements.
It has been found to be particularly advantageous to provide a valve in the fluid path to ensure that fluid only flows between the sub-chambers when a force between the structural elements or the relative speed of the structural elements exceeds a lower limit. This will prevent relative movement of the structural elements unless the force is correspondingly high, with the hydraulic damper allowing damped relative movement of the structural elements only in the event of a particularly high force. Conventional valves achieve this using two valve elements, one of which will be designed as a seat element and the other as a moving element. The seat element is rigidly attached to the piston and comprises at least one section of the fluid path. The moving element rests against the end of the seat element in a way as to close the fluid path when in rest position.
When in rest position, a spring system would normally exert a spring force pressing the moving element against the seat element or the fluid path. The moving element is displaced from its rest position when the pressure difference between the sub-chambers exceeds a lower limit, i.e. when the hydraulic damper is subjected to a force exceeding a lower limit. The pressure difference will in this case exert a force on the moving element that exceeds the force of the spring system, pressing said element away from the seat element to allow fluid to flow between the sub-chambers via the fluid path, i.e. from a first sub-chamber at high pressure to a second sub-chamber at a lower pressure.
Conventional hydraulic dampers, however, have the disadvantage that the valves will suddenly open when the force between the structural elements exceeds the lower limit, potentially causing jerking displacements of the structural elements. In addition, conventional hydraulic dampers are only suited for damping forces between the structural elements they are attached to if those forces remain within a certain limited range. This is because the valves in the piston will not open if the force on the hydraulic damper is too low and the piston then cannot or can hardly move in its working chamber, with no damping effect. If hydraulic dampers experience a very large force, then conventional hydraulic dampers will not allow adequate relative displacement of the construction elements, since they cannot follow large forces fast enough to prevent structural damage.
This inherent problem with conventional hydraulic dampers is due to the fact that the design of hydraulic dampers is subject to a compromise with regard to setting the minimum force beyond which damping will be ensured and setting the resilience of the hydraulic damper in case very large forces are applied.